Method for manufacturing metal nanopowder by wire-explosion and apparatus for manufacturing the same

ABSTRACT

There are provided a method and an apparatus for manufacturing a metal nanopowder having a uniform particle size distribution by uniformly applying current to a center portion of the metal wire and a surface portion thereof. The method includes increasing a surface roughness of a metal wire; supplying the metal wire having the increased surface roughness to an electrode in a reaction chamber; and wire-exploding the metal wire by supplying electrical energy to the electrode.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of Korean Patent Application No. 10-2013-0076064 filed on Jun. 28, 2013, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a metal nanopowder by wire-explosion and an apparatus for manufacturing the same, and more particularly, to a method for manufacturing a nanopowder having a uniform particle size distribution by uniformly applying electrical energy to a metal wire, and an apparatus for manufacturing the same.

2. Description of the Related Art

Technology has moved in a direction in which devices and components are small-sized, lightweight, and have high strength, due to industrial improvements. One method capable of satisfying the functions is to manufacture a device and a component using nanoparticles.

In general, nanoparticles have a diameter of 1 nm to 100 nm, and even in the case that a material formed of the nanoparticles has the same chemical composition and the same physical crystallization structure, the material formed of nanoparticles may have specific physical properties which are not evident in an existing material.

Nanoparticles have great industrial potential in fields such as the field of electronic components, the field of materials of living, the field of medicine, the field of national defense, the field of energy generation, the field of environmental materials, and the like, due to the specific physical properties thereof, and as certain nanoparticles have been commercialized, their value has been confirmed.

Unlike the positive aspects as described above, nanoparticles have problems to which solutions are sought, and for example, nanoparticles may have difficulties in terms of dispersibility due to having a large specific surface area, difficulties in terms of chemical stability regarding particle oxidation, and difficulties in terms of obtaining nanoparticles having a uniform size in a manufacturing process thereof.

As a method for synthesizing nanoparticles, a chemical synthesis method is mainly used. However, in consideration of industrial improvements and environmental aspects such as global warming, the chemical synthesis method has disadvantages in that contamination caused by impurities, the generation of chemical by-products such as waste solutions, dangers in handling chemical materials, and the like may occur.

Therefore, systems which are environmentally friendly and are capable of mass producing a nanopowder by using a vapor method have been studied and developed, and as a method having a high possibility for enabling mass-production, physical methods such as a plasma heating method, a pulsed wire discharge (PWD) method, and the like, may be used.

The pulsed wire discharge (PWD) method is a method in which, after a capacitor is charged with current, a power pulse is produced using high voltage to instantaneously discharge electrical energy into a metal wire, such that the metal is evaporated and condensed to produce the nanopowder. A flowchart in which wire in a solid-phase is vaporized to form the nanopowder is illustrated in FIG. 1.

The pulsed wire discharge (PWD) method may be utilized for use with all metals and alloys capable of being formed into wire, and may be easily used in producing oxides and nitrides by using oxygen or nitrogen in the atmosphere of the process. In general, the discharge process takes 10⁻⁶ seconds, and 10⁶ W of power is consumed during this short period of time. The pulsed wire discharge (PWD) method is appropriate for producing nanopowder particles having a size of 50 nm to 150 nm.

However, in the pulsed wire discharge (PWD) method according to the related art, a nanopowder having a particle size distribution of several nm is produced on a surface portion of the metal wire, but a nanopowder having a particle size distribution of several μm is produced in the center portion thereof.

The reason that nanoparticles having a non-uniform particle size distribution are produced is because an electric field flowing through the wire is not constant. In wire having a smooth surface, the extent of disturbance with respect to current flow is different between the surface portion of the metal wire and the center portion thereof due to a skin effect, such that the surface portion thereof is initially exploded and the center portion is subsequently exploded. Here, the evaporation in the center portion is not smooth, such that it may be difficult to produce nanopowder particles, and therefore, relatively large micro-sized particles are produced. The reason for this is that the current flow is small in the center portion of the metal wire, such that Joule heating is also low.

The manufactured nanopowder having the non-uniform particle size distribution requires filtering having a high resolution and a sorting process using centrifugal force in the subsequent process, such that the process may be complicated and costs increased.

Therefore, a method for synthesizing a nanopowder having a uniform particle size distribution by uniformly supplying electrical energy to a metal raw material in the pulsed wire discharge (PWD) method has been demanded.

Patent Document 1, which is directed to an apparatus for the production of a metal nanopowder by wire-explosion, is characterized by mounting a vibrator on a feeding unit to allow a particle size of a nanopowder produced according to a position of a wire to be uniform, through a mechanical resonance phenomenon and vibration of atoms and electrons.

[Related Art Document] (Patent Document 1) Korean Patent Laid-Open Publication No. 10-2011-0122277 SUMMARY OF THE INVENTION

An aspect of the present invention provides a method for manufacturing a metal nanopowder having a uniform particle size distribution by wire-explosion by uniformly applying current to a center portion of a metal wire and a surface thereof, and an apparatus for manufacturing the same.

According to an aspect of the present invention, there is provided a method for manufacturing a metal nanopowder by wire-explosion, the method including: increasing a surface roughness of a metal wire; supplying the metal wire having the increased surface roughness to an electrode in a reaction chamber; and wire-exploding the metal wire by supplying electrical energy to the electrode.

The increasing of the surface roughness Ra of the metal wire may be performed to cause the surface roughness of the metal wire to be in a range of 0.2 μm to 6.3 μm.

The increasing of the surface roughness Ra of the metal wire may be performed by at least one selected from the group consisting of a honing process, a polishing process, a turning process, and a milling process.

The metal wire may include at least one selected from a group consisting of copper, nickel, aluminum, iron, gold, and silver.

The metal wire may have a diameter of 0.01 to 10 mm.

A pulse voltage of 1 to 100 kV may be applied to the electrode for 1 μs to 10 μs.

According to another aspect of the present invention, there is provided an apparatus for manufacturing a metal nanopowder by wire-explosion, the apparatus including: a high voltage electrode having high voltage electrical energy applied thereto to wire-explode a metal wire; a feeding unit supplying the metal wire to the high voltage electrode; and a surface roughness controlling unit mounted on at least one side of the feeding unit and increasing the surface roughness of the metal wire.

The surface roughness controlling unit may perform at least one selected from a group consisting of a honing process, a polishing process, a turning process, and a milling process.

The surface roughness controlling unit may include a pair of compression rollers having protrusions formed on a surface thereof, and the metal wire may be compressed by the pair of compression rollers, such that the surface roughness of the metal wire is increased.

The surface roughness controlling unit may be included in the feeding unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a flowchart illustrating a process of manufacturing a nanopowder by wire-explosion;

FIG. 2 is a view illustrating examples of metal wire before and after surface roughness (Ra) thereof is increased according to an embodiment of the present invention;

FIG. 3 is a flowchart illustrating a mechanism by which a nanopowder having a uniform particle size distribution is manufactured due to increased surface roughness (Ra);

FIG. 4 is a cross-sectional view showing an apparatus for manufacturing a metal nanopowder by wire-explosion according to an embodiment of the present invention;

FIG. 5 is an enlarged perspective view of part A of FIG. 4; and

FIG. 6 is a cross-sectional view illustrating an apparatus for manufacturing a metal nanopowder by wire-explosion according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements .

According to an embodiment of the present invention, in order to allow current flows in a surface portion and in a center portion of a metal wire to be uniform, a surface roughness (Ra) of the metal wire may be increased to increase resistance on the surface thereof. Therefore, current flow may be uniform in the surface portion and the center portion of the metal wire, and a metal nanopowder having a uniform particle size distribution may be manufactured.

More specifically, a method for manufacturing a metal nanopowder by wire-explosion according to an embodiment of the present invention includes increasing a surface roughness Ra of a metal wire; supplying the metal wire having the increased surface roughness Ra to an electrode within a reaction chamber; and wire-exploding the metal wire by supplying electrical energy to the electrode.

First, the increasing of the surface roughness Ra of the metal wire will be described.

FIG. 2 is a view illustrating examples of metal wire before and after the surface roughness (Ra) thereof is increased according to an embodiment of the present invention. As shown in FIG. 2, the metal wire having a smooth surface may have various concave-convex shapes through the increasing of the surface roughness Ra. As long as the surface roughness Ra is increased to thereby increase a distance for which current flows, the concave-convex shapes are not particularly limited, in addition to the shapes shown in FIG. 2.

In the metal wire having the increased surface roughness Ra as described above, the length of the surface of the metal wire may be increased, and resistance disturbing the flow of current flowing on the surface may be increased. As a result, the surface portion and the center portion of the metal wire may have the uniform current flow, and wire-explosion may be uniformly induced to manufacture a metal nanopowder having a uniform particle size distribution. FIG. 3 is a flowchart illustrating a mechanism by which a nanopowder having a uniform particle size distribution is manufactured due to increased surface roughness (Ra).

In order to induce uniform current flows in the surface portion and the center portion of the metal wire, the surface roughness Ra of the meta wire may be increased to be 0.2 μm to 6.3 μm.

In the case in which the surface roughness Ra of the metal wire is less than 0.2 μm, the surface resistance thereof may not be sufficiently increased to generate a difference in current flows in the surface portion and the center portion, and in the case in which the surface roughness Ra of the metal wire is greater than 6.3 μm, the metal wire may be locally discharged and may be cut, resulting in a failure in the manufacturing of the nanopowder.

A method for increasing the surface roughness Ra of the metal wire is not specifically limited as long as the surface roughness Ra can be increased in order to apply a uniform electric field to the surface portion and the center portion of the metal wire, and more specifically, the surface roughness Ra of the metal wire may be increased by a honing process, a polishing process, a turning process, and a milling process.

The metal wire of which the surface roughness Ra is to be increased is not specifically limited, and for example, copper, nickel, aluminum, iron, gold, or silver, an alloy or mixture thereof may be used. A diameter of the metal wire may be 0.01 mm to 10 mm, and a length thereof is not specifically limited.

Then, the metal wire having the increased surface roughness Ra may be supplied to the electrode within the reaction chamber.

Two electrodes for wire-explosion may be provided in the reaction chamber, such that the wire-explosion may occur in the reaction chamber. The metal wire having the increased surface roughness Ra may be supplied between two electrodes in the reaction chamber by a wire feeding unit.

After the metal wire is supplied between two electrodes, the electrical energy may be supplied to the electrodes, thereby wire-exploring the metal wire, and thus, the metal nanopowder is manufactured.

The wire-explosion may occur by applying a pulse voltage to the metal wire n times (n is a natural number) using two electrodes. Here, N is not specifically limited.

The pulse voltage may be supplied at an interval of 0.5 to 10 seconds, and the period of the pulse voltage may be constant in the above-described range or may be changed. For example, the pulse voltage may be 1 kV to 100 kV, and may be constant in the above range or may be changed. The pulse voltage may be applied for 1 μs to 10 μs.

The current flow may be generated to be uniform in the surface portion and the center portion of the metal wire having the increased surface roughness Ra, such that a metal nanopowder to be manufactured according to a position of the wire may obtain a uniform particle size distribution.

Then, an apparatus for manufacturing a metal nanopowder by wire-explosion according to an embodiment of the present invention will be described.

FIG. 4 is a cross-sectional view illustrating an apparatus for manufacturing a metal nanopowder by wire-explosion according to an embodiment of the present invention.

Referring to FIG. 4, a reaction chamber 100 in which wire-explosion occurs may include a wire feeding unit in an upper portion thereof. The wire feeding unit may include a wire roller 21 having a metal wire M wound therearound and a pair of guide rollers 22 feeding the metal wire M unwound from the wire roller 21 in a direction toward a high voltage electrode 50 positioned at a lower portion of the reaction chamber 100.

The metal wire M fed in the direction toward the high voltage electrode 50 by the guide rollers 22 may pass through a wire guide 40 having a hollow portion therein. In other words, a route of the metal wire M may be determined by the wire guide 40 so as to be fed to the vicinity of the high voltage electrode 50. When pulse power is applied to the high voltage electrode 50, the pulse power may be supplied to the metal wire, such that the metal wire may be wire-exploded to be vaporized. The metal wire may be vaporized, and cooled/condensed to manufacture a nanopowder.

However, as described above, in the case of a metal wire having a smooth surface, the extent of disturbance with respect to current flow is different between the surface portion of the metal wire and the center portion thereof due to a skin effect, such that particle sizes of a powder to be manufactured may not be uniform between the surface portion of the metal wire and the center portion thereof. In order to solve the above-described problem, the apparatus for manufacturing a metal nanopowder by wire-explosion according to the embodiment of the invention may include a surface roughness controlling unit increasing the surface roughness Ra of the metal wire.

As shown in FIG. 4, the surface roughness controlling unit according to the embodiment of the invention includes a pair of compression rollers 31 having protrusions formed on a surface thereof. Referring to FIG. 5, an enlarged view of part A of FIG. 4, it may be appreciated that the metal wire M passes through between the pair of compression rollers 31 having the protrusions formed on the surface thereof, and is compressed, such that the surface roughness Ra of the metal wire is increased.

The surface roughness controlling unit according to the embodiment of the invention is not limited to the compression rollers 31 having the protrusions formed on the surface thereof as shown in FIG. 4, and as long as a configuration enables the surface roughness of the metal wire M to be increased, and a honing process, a polishing process, a turning process, a milling process, or the like, may be performed.

In FIG. 4, the compression rollers 31 are disposed beyond the guide rollers 22 of the wire feeding unit, but the position thereof is not limited thereto. The surface roughness controlling unit may be mounted on one side of the wire feeding unit before the metal wire is supplied to the high voltage electrode 50.

In addition, as shown in FIG. 6, while the metal wire M unwound from the wire roller 21 may be fed to the compression rollers 32 having the protrusions formed on the surface thereof, the surface roughness Ra thereof may be simultaneously increased. That is, the surface roughness controlling unit may be included in the wire feeding unit.

In the metal wire having the increased surface roughness by the surface roughness controlling unit, surface resistance may be increased and as a result, the current flow may be disturbed at the surface thereof, such that electric energy may be uniformly applied to the surface portion of the metal wire and the center portion thereof to allow the particle size of the manufactured metal nanopowder to be uniform.

As set forth above, in a method and an apparatus for manufacturing a metal nanopowder by wire-explosion according to embodiments of the invention, current may be uniformly applied to a center portion of the metal wire and a surface portion thereof, whereby a metal nanopowder having a uniform particle size distribution can be manufactured.

While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims. 

What is claimed is:
 1. A method for manufacturing a metal nanopowder by wire-explosion, the method comprising: increasing a surface roughness of a metal wire; supplying the metal wire having the increased surface roughness to an electrode in a reaction chamber; and wire-exploding the metal wire by supplying electrical energy to the electrode.
 2. The method of claim 1, wherein the increasing of the surface roughness of the metal wire is performed to cause the surface roughness of the metal wire to be in a range of 0.2 μm to 6.3 μm.
 3. The method of claim 1, wherein the increasing of the surface roughness of the metal wire is performed by at least one selected from the group consisting of a honing process, a polishing process, a turning process, and a milling process.
 4. The method of claim 1, wherein the metal wire includes at least one selected from the group consisting of copper, nickel, aluminum, iron, gold, and silver.
 5. The method of claim 1, wherein the metal wire has a diameter of 0.01 mm to 10 mm.
 6. The method of claim 1, wherein a pulse voltage of 1 kV to 100 kV is applied to the electrode for 1 μs to 10 μs.
 7. An apparatus for manufacturing a metal nanopowder by wire-explosion, the apparatus comprising: a high voltage electrode having high voltage electrical energy applied thereto to wire-explode a metal wire; a feeding unit supplying the metal wire to the high voltage electrode; and a surface roughness controlling unit mounted on at least one side of the feeding unit and increasing the surface roughness of the metal wire.
 8. The apparatus of claim 7, wherein the surface roughness controlling unit performs at least one selected from the group consisting of a honing process, a polishing process, a turning process, and a milling process.
 9. The apparatus of claim 7, wherein the surface roughness controlling unit includes a pair of compression rollers having protrusions formed on a surface thereof, and the metal wire is compressed by the pair of compression rollers, such that the surface roughness of the metal wire is increased.
 10. The apparatus of claim 7, wherein the surface roughness controlling unit is included in the feeding unit. 